1. Field of the Invention
This invention relates to the field of visual inspection and testing of micro-electronic chips. More particularly, the invention pertains to an apparatus for expediently locating the chip, seated in a cavity, to begin an accurate visual analysis of its surfaces.
2. Description of the Prior Art
The recent downsizing of micro-electronic chips and the high demand for these chips, necessitates the need for fast, accurate and economical testing of their physical and electrical properties. In order to test the chips more efficiently, it is necessary to first eliminate visibly flawed chips from the production line so that later electrical testing is conducted only on visibly acceptable chips. Examples of such visually observable flaws are delamination of the dielectric body, cracks in the chip's exterior and flaws in the metal termination such as smears, and spillovers, and unacceptable waviness. Visual inspection apparatuses are used in the industry to test these physical properties. These apparatuses generally include camera devices for observing the chip, software processing devices for detecting and recording the flaws, and bright light sources, for illuminating the chip.
Prior art visual inspection devices have not been able to accurately and efficiently observe the chip because of high specularity values of the chip and surrounding materials. Specularity of a material describes the size and brightness of specular highlights it reflects. Smooth, reflective objects have highlights that are small and bright. Rough, reflective objects have highlights that are large and diffuse, but still bright. Less reflective objects, rough or smooth, have dimmer highlights. Usually, conventional metallic materials, such as aluminum, stainless steel, titanium etc., that are used to make load wheels to house the chip during the visual inspection process, create significant specular highlights due to normal wear and tear and accumulation of foreign matter on the metals. Certain treatments and coatings can be used to reduce the apparent specularity of these surfaces but these remedies are temporary and deteriorate over time. The replacement of these metals with plastic-based or other similar materials is ineffective because the inherent weaker physical properties of the plastic materials will cause them to wear out over time.
The high degree of specularity around the exposed surface of the chip and its surrounding environment, makes it difficult to electronically visualize exactly where the chip is located in the chip-holding cavity in order for the software program to start the visual test on the chip. The brightness and light reflection of the surrounding environment blend with that of the chip and makes it virtually impossible to accurately distinguish the chip from the rest of its environment, especially under high speed processing conditions where residence time of the chip in the cavity is measured in microseconds. Therefore, absent a point of reference, the software program cannot start visual testing of the chip, or may start the visual testing process at an erroneous point of reference.